Where will trees grow in a new climate?

Researchers at the World Agroforestry Centre Philippines have created a model that suggests where threatened trees are likely to grow under a future climate, say Kristine Garcia, Rodel Lasco, Amor Ines, Bradfield Lyon and Florencia Pulhin

One of the aspects that scientists look at to evaluate the potential impacts of climate change on natural systems is the likely shift in the geographic distribution and habitats of various species.

Where trees will live, and die, under new climates can now be more easily predicted. Photo: World Agroforestry Centre/Meine van Noordwijk

We set out to assess these shifts for 14 threatened forest tree species in the Philippines, expecting that the results would be useful for developing conservation strategies. They could provide better options in areas that are continuously pressured by human activities and also potentially by climate change. Our study was the first attempt in the country to assess the impacts of climate change on forest ecosystems at the species level. The study was even more important insomuch as threats from anthropogenic activities and climate change could be exacerbated by a shortage of research and conservation interest. Only two studies on related subjects have been conducted since 1997.

Using a machine algorithm called Maxent, which is based on the principle of maximum entropy, we found that the distribution of the tree species would be largely determined by biophysical variables (80%) rather than bioclimatic variables (20%). What this means is that the quality of the soils in the trees’ habitats would be very important to their survival under a changing climate. However, it does not necessarily mean that biophysical variables are more important than bioclimatic ones because impact would depend on specific location and time. It does suggest that soils need to be comprehensively classified and climate factors, such as rainfall and temperature, integrated into the classification system.

We also need to bear in mind that the seemingly low importance of the bioclimatic variables could be a result of restricted parameters in the computer model we used based on the outcome of the spatial autocorrelation. There might be some bioclimatic variables that could have provided further explanation that were not included in the final modelling process. This implies that having inaccurate predicted distribution could impede the success of conservation management efforts. As such, expert knowledge of the ecological niche of the species should be taken into account as much as possible during identification and selection of environmental variables.

We also found that seven species (Afzelia rhomboidea; Koordersiodendron pinnatum; Mangifera altissima; Shorea contorta; Shorea palosapis; Shorea polysperma; Vitex parviflora) were likely to benefit from a warmer and wetter future climate owing to the potential increase in their suitable habitat while the other seven species (Agathis philippinensis; Celtis luzonica; Dipterocarpus grandiflorus; Shorea guiso; Shorea negrosensis; Toona calantas; Vatica mangachapoi) would probably decline.

Other implications of our study are that the possible alterations to habitat by future climate mean that appropriate adaptation strategies are needed to conserve those areas where the threatened species are likely to be found in the future.Whatsmore, any claimed ‘positive’ and ‘negative’ impacts of climate change should be treated with caution. It would be better to see the impacts as an opportunity to implement appropriate adaptation strategies. For instance, the potential increase in suitable habitat for some species will help them endure the manifold pressures arising from climate change. Therefore, existing and predicted habitat areas of the threatened species should be protected from clearing, encroachment and further degradation. Another option is to provide functional connectivity between smaller patches of forest through restoration and maintenance of links between them. Owing to the inherent connectivity between different ecosystems in a landscape, it is imperative that the biodiversity of species is protected so that the landscape can sustainably provide the services people need.

There are still major gaps in knowledge about the impacts of climate change on forests, associated wildlife and people and how adaptation measures can best be tailored to local conditions. The advancement of our understanding in how to model the distribution of species in the face of future climate and the improvement of spatial databases could lead to development of science-based conservation strategies that would benefit both the species and their ecosystems. We need to double our efforts to protect those species that are exposed to different threats, including climate change.

This article is one of the products of the recently concluded USAID-funded project, Mainstreaming Climate Change in Biodiversity Planning and Management in the Philippines, implemented by the World Agroforestry Centre Philippines.

Robert Finlayson is the Southeast Asia program's regional communications specialist. As well as writing stories for the Centre's website, he devises and supervises strategies for projects and the countries in the Southeast Asia region, including scripting and producing videos, supervising editors and translators and also assisting with resource mobilization.